1. Field of the Invention
The invention relates to a transmitting/receiving station which is constructed to cooperate with at least one transponder and by means of a which a transmitting mode and a receiving mode can be carried out and which includes the means specified hereinafter, i.e. a transmission coil circuit comprising a transmission coil for the communication with a transponder transmission coil provided in a transponder, conductor means having a given characteristic impedance, which conductor means have a first end and a second end and are connected to the transmission coil circuit at the location of their second end, transmitting means which are constructed to generate a request signal which in a transmitting mode can be transmitted by the transmission coil and can be received by a transponder and which are connected to the conductor means at the location of the first end of the conductor means, and receiving means which are constructed to receive an answer signal produced in the transmitting/receiving station by a transponder in response to a request signal received by it and which are also connected to the conductor means at the location of the first end of the conductor means.
2. Description of the Related Art
Such a transmitting/receiving station of the type defined in the opening paragraph is known from the document EP 0 492 569 A2. In the known transmitting/receiving station care has been taken that in a transmitting mode the transmitting means transmit a request signal with a maximal energy content is transmitted to the transmission coil circuit and eventually to the transmission coil in order to enable a request signal with a maximal energy content to be transmitted to a transponder situated within the receiving range of the transmitting/receiving station. For this purpose the known transmitting/receiving station has an impedance matching network arranged between the conductor means, which are formed by a coaxial cable having a given characteristic impedance, and the transmission coil, as a result of which substantially no undesired reflections occur at the location of the second end of the conductor means, which reflections could give rise to a reduction of the energy content of the request signal transmitted to the transmission coil. In order to enable a request signal having a maximal energy content to be fed into the conductor means by the transmitting means, it is customary in such a known transmitting/receiving station to assure that the internal resistance and hence the output impedance of the transmitting means differs distinctly from the characteristic impedance or surge impedance of the conductor means, so that the internal resistance of the transmitting means causes only insignificant losses of the energy content of a request signal.
In the known transmitting/receiving station the transmitting means as well as the receiving means are connected to the conductor means at the location of the first end of the conductor means, respectively in order to generate a request signal and to receive an answer signal. Owing to this configuration the problem arises that for an answer signal produced in the transmitting/receiving station and transmitted from the transmission coil to the receiving means via the conductor means a rather unfavorable impedance mismatch exists between the conductor means and the receiving means, as a result of which strongly varying matching conditions occur at the second end of the conductor means, i.e. at the end near the transmission coil, as a function of the instantaneous conductor length of the conductor means, which in its turn results in the input resistance, seen by the transmission coil via the matching network, in the conductor means at the location of the second conductor means depends strongly on the conductor length of the conductor means, so that strongly varying attenuation conditions for the answer signal produced in the transmitting/receiving station occur at the location of the second end of the conductor means. Ultimately, these unfavorable conditions have the adverse effect that an answer signal - produced in the transmitting/receiving station by a transponder which communicates with this station - can only be received in an unsatisfactory manner by the receiving means, which is unfavorable for a reliable and correct communication of the transmitting/receiving station with transponders and which is therefore undesirable.
It is an object of the invention to preclude the afore-mentioned problems and to provide an improved transmitting/receiving station which guarantees improved reception characteristics.
According to the invention, in order to achieve the afore-mentioned object in a transmitting/receiving station of the type defined in the opening paragraph, additional means are interposed between the transmitting means and the receiving means and the first end of the conductor means, by which additional means the transmitting means and the receiving means are connected to the first end of the conductor means and by which additional means the first end of the conductor means has a matched termination for an answer signal produced in the transmitting/receiving station.
With simple means and only comparatively low additional expense the measures in accordance with the invention yield the great advantage that always the same good receiving conditions, which remain always constant and are independent of the conductor length of the conductor means, are obtained for an answer signal produced in a transmitting/receiving station in accordance with the invention by a transponder. This guarantees that the receiving means of a transmitting/receiving station in accordance with the invention are practically always supplied with an answer signal having a comparatively high energy content, which is advantageous for an error-free and correct processing of such an answer signal. The reception of an answer signal having a comparatively high energy content by the receiving means is of great importance because an answer signal produced in a transmitting/receiving station by a transponder lies within a range of a distinctly lower amplitudes in relation to a request signal, as a result of which amplitude losses are particularly unfavorable. The measures in accordance with the invention have the advantage that they enable the use of conductor means having a conductor length which is distinctly higher than a quarter of the wavelength of a carrier signal used in a transmitting/receiving station in accordance with the invention.
A transmitting/receiving station in accordance with the invention having the characteristic features defined in the independent Claim 1 may include additional means of a more intricate and therefore comparatively expensive construction. However, in this respect it has proved to be advantageous in a transmitting/receiving station in accordance with the invention having the characteristic features defined in the independent claim 1 if the measures defined in the dependent claim 2 are taken. This yields the advantage of a low-cost construction realized by a minimal number of means which are as simple as possible.
In a transmitting/receiving station having the characteristic features defined in the dependent claim 2 it has proved to be advantageous if, in addition, the measures defined in the dependent claim 3 are taken. Such an embodiment has proved to be particularly advantageous in practice and is moreover particularly simple.
In a transmitting/receiving station having the characteristic features defined in the dependent claim 2 it has proved to be advantageous if, in addition, the measures defined in the dependent claim 4 are taken. Thus, it is achieved in a simple manner that by a suitable choice of the numbers of turns of the transformer coils the determinative resistances of the transmitting means and the receiving means as well as the conductor means can simply be matched to one another and can thus be chosen from comparatively wide ranges. Moreover, it is thus achieved that the values of the components of the filter means can be selected from ranges which are favorable in view of a simple circuit design and a low-cost and problem-free implementation. It is to be noted that the measures defined in the dependent claim 4 can also be applied advantageously in a transmitting/receiving station having the characteristic features defined in claim 3.
In a transmitting/receiving station having the characteristic features defined in the dependent claim 4 it has proved to be very advantageous if, in addition, the measures defined in the dependent claim 5 are taken. Thus, the advantages of the use of a ferrite core in a matching transformer, which advantages are known per se, are also obtained in a transmitting/receiving station in accordance with the invention, which advantageously results in an intimate inductive coupling between the three transformer coils.
In a transmitting/receiving station having the characteristic features defined in the dependent claim 4 it has further proved to be advantageous if, in addition, the measures defined in the dependent claim 6 are taken. Thus, the advantages of the use of a such compensating capacitors, which are known per se, are also obtained in a transmitting/receiving station in accordance with the invention, in which the effect of such compensating capacitors has proved to be particularly useful. It is to be noted that the measures defined in the dependent claim 6 can also be applied advantageously in a transmitting/receiving station having the characteristic features defined in claim 5.
The afore-mentioned aspects as well as further aspects of the invention will be apparent from the embodiments described hereinafter by way of examples and will be elucidated with reference to these embodiments.